2011-12-19

Opportunity Sol 1032 (Spirit Sol 1053)

Yestersol's drive didn't go quite as planned. Opportunity drove through a small depression that increased her tilt to 7.44deg -- just above her tilt limit of 7deg -- so she stopped, which of course was the right thing to do. But she's actually fine, and ready to continue.[1]

The remainder of the drive is only about 8m, and that stops us in a perfectly safe position, about 2m from the rim. But there's a ritual now: any rim approach causes some people to panic, and after a lengthy discussion, we end up moving the final position back another 50cm. Which is how it always happens. It's just silly: we're not going to be wrong by 2m over a drive of 8m, and even if we were, we have reactive checks -- such as the tilt limit that correctly stopped us today -- that would catch our mistake before the vehicle was in danger. The 50cm pullback is just a compromise to end the discussion, nothing more.

What bugs me about this most, I think, is the fact that the extra 50cm of buffer is there not for any technical reason but to mollify the exaggerated concerns of people who aren't RPs. There, I said it. It feels good to have it said.

Tomorrow, no doubt, the ritual will be performed again.

[Next post: sol 1063 (Opportunity sol 1045), December 30.]

[1] One of the hazards of the job, I'm afraid. You always want to pick a tilt limit that's just a little higher than you think the rover will actually experience, so that an excessive tilt will mean she's strayed off course. But it doesn't always work like that: faulty data or other problems can lead you to choose a number that's lower than you should have. Fortunately, nearly all the time -- as in this case -- the problem with being overly conservative is just slight embarrassment. As long as I still have a rover to play with the next day, I can take it.